Light-sensitive 1,2 quinone diazide containing mixture and light-sensitive copying material prepared therefrom wherein imaged produced therein is visible under yellow safety light

ABSTRACT

Disclosed is a light-sensitive mixture comprising (a) a 1,2-quinonediazide or a mixture of (a 1 ) a compound forming an acid on exposure and (a 2 ) a compound having at least one C--O--C bond cleavable by acid; (b) a water-insoluble binder soluble in aqueous-alkaline solutions; (c) an organic compound forming an acid on exposure of the general formula I ##STR1## in which X is a single bond or one of the groups CO, SO 2 , N=N or CR 7  R 8 , R 1 , R 2 , R 3  and R 4  are hydrogen atoms, halogen atoms or nitro groups, with not more than two of these radicals being hydrogen atoms and at least one thereof being a nitro group, R 5  and R 6  are hydrogen atoms or 1,2-naphthoquinone-2-diazide-4-sulfonyloxy radicals, with R 5  and R 6  being always different from each other, and R 7  and R 8  are hydrogen atoms or lower alkyl radicals, and (d) an azo dyestuff containing at least one nitro group in the molecule. Also disclosed are printing plates and photoresists prepared with the light-sensitive mixtures.

BACKGROUND OF THE INVENTION

The present invention relates to a light-sensitive mixture, whichbecomes soluble by exposure, comprising

(a) a 1,2-quinonediazide or a mixture of

(a¹) a compound forming an acid on exposure and

(a²) a compound having at least one C--O--C bond cleavable by acid,

(b) a water-insoluble binder soluble in aqueous-alkaline solutions,

(c) an organic compound forming an acid on exposure, and

(d) a dyestuff.

After exposure, the mixture shows a clearly visible color contrastbetween exposed and unexposed areas.

Mixtures of the generic type indicated are preferably used for preparingplanographic printing plates and photoresists, and such mixtures areknown, for example, from U.S. Pat. No. 3,969,118. The mixtures describedthere contain as the dyestuff (d) a triphenylmethane, azine oranthraquinone dyestuff and as acid forming organic compound (c) a1,2-naphthoquinone-2-diazide-4-sulfonyl halide. After image exposurethey produce an image contrast which is clearly visible in daylight orin white artificial light. However, the image contrast is lesspronounced, and in some cases inadequate under the yellow safety lightcustomarily used when working with reprographic materials.

U.S. Pat. No. 3,929,488 describes corresponding mixtures which containcertain azo dyestuffs as the dyestuffs and diazonium salts of strongacids as the acid donors. These mixtures produce only a relativelyslight visual contrast in normal light and in safety light.

U.S. Pat. No. 4,163,672 and British Pat. No. 2,005,855 describe similarmixtures which contain diazonium salts as the acid donors and azo,triphenylmethane, azine or anthraquinone dyestuffs as the dyestuffs.Their contrast is likewise frequently inadequate in yellow safety light.

U.S. Pat. No. 4,160,671 describes corresponding mixtures which containtrihalogenomethyl-s-triazines or trihalogenomethyl-2-pyrones as the aciddonors and azine, triphenylmethane or anthraquinone dyestuffs as thedyestuffs. The properties of these mixtures are similar to those of theabovementioned mixtures.

British Pat. No. 2,038,810 describes mixtures which contain as aciddonors 1,2-naphthoquinone-2-diazide-4-sulfonic acid esters or amides ofphenols or aromatic amines, which have electron-attracting substituentsin the benzene nucleus. Preferred substituents are halogen atoms andnitro groups. The dyestuffs mentioned include triphenylmethane dyestuffsand oil-soluble dyestuffs. These mixtures produce color contrasts whichare better discernible under yellow light than those produced by some ofthe other mixtures mentioned above; however, contrast still does notmeet all requirements.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide animproved positive-working, light-sensitive mixture of the generic typedescribed at the outset and which after imagewise exposure displays animage of the original which is better visible under yellow safety lightthan in the case of the previously proposed mixtures.

In particular, it is an object of the invention to provide such amixture which after imagewise exposure displays a contrast-rich image ofthe original which is clearly visible even under yellow safety light.

A further object of the invention resides in providing an improvedcopying material utilizing the light-sensitive mixture of the invention.

In accomplishing the foregoing objects, there has been provided inaccordance with one aspect of the present invention a light-sensitivemixture comprising (a) a 1,2-quinonediazide or a mixture of (a¹) acompound forming an acid on exposure and (a²) a compound having at leastone C--O--C bond cleavable by acid, (b) a water-insoluble binder solublein aqueous-alkaline solutions, (c) an organic compound forming an acidon exposure comprising an ester of the general formula I ##STR2##wherein X is a single bond or one of the groups CO, SO₂, N=N or CR⁷ R⁸

R¹, R², R³ and R⁴ are hydrogen atoms or halogen atoms or nitro groups,with not more than two of these groups being hydrogen atoms and at leastone thereof being a nitro group,

R⁵ and R⁶ are hydrogen atoms or1,2-naphthoquinone-2-diazide-4-sulfonyloxy radicals, with R⁵ and R⁶being always different from each other, and

R⁷ and R⁸ are hydrogen atoms or lower alkyl radicals, and (d) a dyestuffcomprising an azo dyestuff containing at least one nitro group in themolecule.

In accordance with another aspect of the invention, there has beenprovided a light-sensitive copying material comprising a support and alight-sensitive layer which becomes soluble in a developer on exposureand comprises a light-sensitive mixture as defined above.

Further objects, features and advantages of the present invention willbecome apparent from the detailed description of preferred embodimentswhich follows.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention relates to a light-sensitive mixture comprising

(a) a 1,2-quinonediazide or a mixture of

(a¹) a compound forming an acid on exposure and

(a²) a compound having at least one C--O--C bond cleavable by acid,

(b) a water-insoluble binder soluble in aqueous-alkaline solutions,

(c) an organic compound forming an acid on exposure and

(d) a dyestuff.

In the mixture according to the invention, the dyestuff is an azodyestuff containing at least one nitro group in the molecule and thecompound (c) forming an acid on exposure is an ester of the generalformula I ##STR3## in which X is a single bond or one of the groups CO,SO₂, N=N or CR⁷ R⁸,

R¹, R², R³ and R⁴ are hydrogen atoms, halogen atoms or nitro groups,with not more than two of these radicals being hydrogen atoms and atleast one thereof being a nitro group,

R⁵ and R⁶ are hydrogen atoms or1,2-naphthoquinone-2-diazide-4-sulfonyloxy radicals, with R⁵ and R⁶being always different from each other, and

R⁷ and R⁸ are hydrogen atoms or lower alkyl radicals.

The azo dyestuffs contained in the mixture contain at least one, andpreferably 2 or more, nitro groups in the molecule. Monoazo dyestuffs,in particular those formed from substituted benzene-diazonium compoundsand aromatic amines as coupling components, are preferable. The azodyestuffs, in addition to nitro groups, can also contain furthersubstituents. Examples of preferable substituents are amino groups,particularly tertiary amino groups, halogen atoms, alkoxy groups andacylamino groups. Owing to their particularly advantageous colorcontrast, blue azo dyestuffs are generally preferable. The amount of azodyestuff is in general from about 0.5 to 10%, preferably from about 2 to7%, by weight, relative to the nonvolatile constituents of the mixture.

The preferred photolytic acid donors of the formula I are those in whichall radicals R¹ to R⁴ are halogen atoms or nitro groups. The compoundswhich have at least two, particularly those with four nitro groups inthe molecule are especially effective. Preferable halogen atoms are Cland Br, particularly Br. R⁷ and R⁸, if alkyl radicals, generally have 1to 4, preferably 1 or 2 carbon atoms.

Like the known naphthoquinonediazidesulfonic acid esters, the compoundsof formula I are prepared by causing reactive sulfonic acid derivatives,for example, sulfonyl chlorides, to react with the correspondingsubstituted bisphenols. The acid donors are generally added in amountsof from about 1 to 20%, preferably 7 to 15% by weight, relative to thenonvolatile constituents.

The mixtures according to the invention can be stored, in the form oflight-sensitive layers applied to a support or as solutions forpreparing photoresist layers, in the dark over prolonged periods withoutdecomposition. The image contrast obtained by means of the mixturesaccording to the invention is considerably more brilliant than the imagecontrast obtained by means of the same acid donors combined withtriphenylmethane, azine or anthraquinone dyestuffs or with azo dyestuffswhich do not contain nitro groups.

The mixture according to the invention contains as a further essentialconstituent a light-sensitive compound (a) or a light-sensitivecombination of compounds (a¹ +a²) the solubility of which in an aqueousalkaline developer solution is increased on exposure. Thelight-sensitive materials include in particular o-quinonediazides andcombinations of photolytic acid donors with acid-cleavable compounds.

The o-quinonediazides preferably used are1,2-naphthoquinone-2-diazide-4- or -5-sulfonic acid esters or amides. Ofthese, the esters, in particular those of 5-sulfonic acids, areparticularly preferable. Suitable compounds of this type are known andhave been described, for example, in German Pat. No. 938,233 and inGerman Offenlegungsschriften No. 2,331,377 (=U.S. Pat. No. 3,969,118),No. 2,547,905, and No. 2,828,037, the disclosures of which are herebyincorporated by reference.

The amount of o-quinonediazide compounds including the compounds offormula I is in general from about 3 to 50%, preferably from about 7 to35% by weight, relative to the nonvolatile constituents of the mixture.

Materials based on acid-cleavable compounds can also be used withbeneficial effect in the mixture according to the invention.

Copying materials of this type are known and have been described, forexample, in U.S. Pat. Nos. 3,779,778 and 4,101,323, German Pat. No.2,718,254 and German Offenlegungsschriften Nos. 2,829,512, 2,829,511 and2,928,636, the disclosures of which are also incorporated by referenceherein. They contain as acid-cleavable compounds orthocarboxylic acidderivatives, monomeric or polymeric acetals, enolethers or acyliminocarbonates, of which the orthocarboxylic acid derivatives and acetalsare preferable. As radiation sensitive, acid-eliminating compounds theypredominantly contain organic halogen compounds, in particular,s-triazines substituted by halogenomethyl groups. Compounds of theformula I are basically also suitable for this purpose.

Of the orthocarboxylic acid derivatives described in U.S. Pat. No.4,101,323, in particular, the diphenoxymethyl ethers of aliphatic oraromatic hydroxy compounds, the N-diphenoxymethyl derivatives of lactamsand, most preferably, the bis-1,3-dioxan-2-yl ethers of aliphatic diolsare used.

Among the polyacetals described in German Pat. No. 2,718,254 (equivalentto U.S. Pat. No. 4,247,611), those containing aliphatic aldehyde anddiol units are preferable.

Of the polymeric ortho esters described in German OffenlegungsschriftNo. 2,928,636 (equivalent to U.S. Pat. No. 4,311,782), polymers withrecurring 1,3-dioxacyclohex-2-yl alkyl ether units, in which the alkylether group can be interrupted by ether oxygen atoms and is preferablybonded to the 5-position of the adjacent ring, are particularlypreferable.

The amount of acid-cleavable compounds in the light-sensitive mixture isin general between about 8 and 60%, preferably between about 14 and 40%by weight, relative to the nonvolatile constituents of the mixture. Theamount of acid-eliminating compound combined therewith is between about0.1 and 10%, preferably between about 0.2 and 5% by weight.

Light-sensitive mixtures according to the invention preferably alsocontain a polymeric, water-insoluble resinous binder which is soluble inthe solvents used for the mixture according to the invention and is alsosoluble, or at least swellable, in aqueous alkalis.

The novolak condensation resins found suitable in many positive copyingmaterials based on naphthoquinonediazides have been found to beparticularly useful and advantageous as an additive also in the case ofmixtures according to the invention. They promote strong differentiationbetween exposed and unexposed areas of the layer on developing. Thisapplies in particular to relatively highly condensed resins havingsubstituted phenols, for example, cresols, as formaldehyde condensationpartners. Further binders which are alkali-soluble, or swellable inalkali, and which are to be mentioned are natural resins, such asshellac and colophony, and synthetic resins, such as copolymers ofstyrene and maleic anhydride or copolymers of acrylic or methacrylicacid, in particular with acrylates or methacrylates.

The type and amount of alkali-soluble resin can vary according to theintended use. Proportions of the total solids content between about 95and 35%, particularly from about 90-55% by weight, are preferable.Numerous other resins can also be used in the mixture, in addition tothe abovementioned resins, with epoxy resins and vinyl polymers, such aspolyvinyl acetates, polyacrylates, polyvinylacetals, polyvinyl ethers,polyvinyl pyrrolidones and copolymers of their parent monomers beingpreferable. The most advantageous proportion of these resins depends onapplication-related requirements and the effect on the developingconditions and is in general no more than about 20% by weight of thealkali-soluble resin. For special requirements, such as flexibility,adhesion, luster and coloring, the light-sensitive mixture can alsocontain small amounts of substances such as polyglycols, cellulosederivatives, such as ethylcellulose, wetting agents, dyestuffs, adhesionpromoters and finely divided pigments and, if required, UV absorbers.

For coating a suitable support, the mixtures are generally dissolved ina solvent. The choice of solvent must be adapted to the coating methodintended, the layer thickness and the drying conditions. Suitablesolvents for the mixtures according to the invention are ketones, suchas methyl ethyl ketone, chlorinated hydrocarbons, such astrichloroethylene and 1,1,1-trichloroethane, alcohols, such asn-propanol, ethers, such as tetrahydrofuran, alcohol-ethers, such asethylene glycol monoethyl ether, and esters, such as butyl acetate. Itis also possible to use mixtures thereof, which can additionallycontain, for special purposes, solvents such as acetonitrile, dioxane ordimethylformamide. In principle, any solvent can be used which does notreact irreversibly with the layer components. Partial ethers of glycols,in particular ethylene glycol monomethyl ether, are particularlypreferable.

Metals are usually used as supports for layers less than about 10 μmthick. For offset printing plates there can be used bright-rolled,mechanically or electrochemically roughened and, if appropriate,anodized aluminum, which can in addition also have been pretreatedchemically, for example, with polyvinylphosphonic acid, silicates,phosphates or hexafluorozirconates or with hydrolyzed tetraethylorthosilicate, and also multi-metal plates, for example, made ofAl/Cu/Cr or of brass/chrome. To prepare letterpress printing plates, themixtures according to the invention can also be applied to zinc ormagnesium plates as well as to their commercially availablemicrocrystalline alloys for powderless etching processes, and also toetchable plastics, such as polyoxymethylene. Owing to their firmadhesion and etch resistance on copper and nickel surfaces, the mixturesaccording to the invention are suitable for gravure or screen printingforms. The mixtures according to the invention can also be used asphotoresists in the manufacture of printed-circuit boards and inchemical milling processes. Other supports, such as wood, paper, ceramicmaterial, textile and other metals, are also possible for differentapplications, as is understood by those skilled in the art.

Preferable supports for layers more than 10 μm thick are plastic filmswhich, in this case, act as temporary supports for transfer layers.Polyester films, for example, made of polyethylene terephthalate, arepreferable for this purpose. However, polyolefin films, such aspolypropylene, are also suitable.

The support material is coated in a known manner by spin-coating,spraying, dipping, roll-coating, by means of slot dies, knife-coating orby flow coating. The coating of, for example, circuit boards, glass orceramic material and silicon disks can also be effected by the transferof a layer from a temporary support. Exposure is effected with lightsources customary in the industry. Irradiation with electrons or lasersalso represents an imaging possibility known to those skilled in theart.

The aqueous-alkaline solutions of stepped alkalinity, preferably with apH in a range of from about 10-14, which are used for developing andwhich can also contain relatively small amounts of organic solvents orwetting agents remove those areas of the copying layer hit by the lightand thus produce a positive image of the original.

The light-sensitive mixtures according to the invention are preferablyused in the preparation of printing forms, i.e., in particular offset,autotypical gravure and screen printing forms, in photoresist solutionsand in so-called dry resists.

The invention is illustrated in more detail by means of the Exampleswhich follow and in which parts by weight (pbw) are related to parts byvolume (pbv) as the g relates to the cm³. Unless otherwise indicated,percentages are percentages by weight.

EXAMPLE 1

A solution of

1.00 pbw of the esterification product of 1 mole of2,3,4-trihydroxybenzophenone and 3 moles of1,2-naphthoquinone-2-diazide-5-sulfonyl chloride,

6.20 pbw of a cresol-formaldehyde novolak having a softening range of120°-135° C. and an average molecular weight of 1,500,

1.00 pbw of the esterification product of 1 mole of2,2-dihydroxy-3,5,3',5'-tetranitrodiphenylmethane and 2 moles of1,2-naphthoquinone-2-diazide-4-sulfonyl chloride, and

0.40 pbw of a blue azo dyestuff obtained by coupling the diazonium saltof 2,4-dinitro-6-chlorobenzene with2-methoxy-5-acetylamino-N,N-diethylaniline in

40 pbw of ethylene glycol monomethyl ether, and

50 pbw of tetrahydrofuran

was used to coat an electrochemically roughened and anodized aluminumplate. Before application of the light-sensitive copying layer, theanodized support had been treated with an 0.5% strength aqueous solutionof polyvinylphosphonic acid. The dry light-sensitive layer had a weightof 2.30 g/m².

The presensitized material thus prepared was imagewise exposed under atransparent positive original.

While the color of the unexposed areas of the copying layer remaineddeep dark blue, the color of the exposed areas of the layer changed to acolor of yellow to pale brown. The image of the original was clearlyvisible in all details, even in the case of yellow illumination.

To prepare the printing form, the exposed printing plate was developedin a known manner with a 7.3% strength aqueous sodium metasilicatesolution, whereby the exposed areas were removed. The remainingunexposed areas of the layer remained visible with good contrast to theuncolored background.

In Examples 2 to 9, which follow, the procedure of Example 1 wasfollowed, and after exposure of the light-sensitive printing platesobtained, essentially the same good results were obtained in respect ofimage contrast, not only before but also after developing. In theExamples which follow, only the recipes of the coating solutions and thetype of supports used are usually indicated, and further short remarksare added only occasionally.

EXAMPLE 2

Coating solution:

1.00 pbw of the esterification product of 1 mole of2,3,4-trihydroxybenzophenone and 3 moles of1,2-naphthoquinone-2-diazide-5-sulfonyl chloride,

6.20 pbw of the novolak indicated in Example 1,

1.00 pbw of the esterification product of 1 mole of4,4'-dihydroxy-3,5,3',5'-tetranitrodiphenylmethane and 2 moles of1,2-naphthoquinone-2-diazide-4-sulfonyl chloride,

0.30 pbw of an azo dyestuff obtained by coupling the diazonium salt of2,4-dinitro-6-chlorobenzene with2-methoxy-5-acetylamino-N-cyanoethyl-N-hydroxyethyl-aniline,

40.00 pbw of ethylene glycol monomethyl ether, and

50.00 pbw of tetrahydrofuran.

Support: electrochemically roughened and anodized aluminum platecorresponding to Example 1.

Color of the exposed areas changed from deep dark blue to yellow brown.

EXAMPLE 3

Coating solution:

0.70 pbw of the esterification product of 1 mole of2,3,4-trihydroxybenzophenone and 2 moles of1,2-naphthoquinone-2-diazide-5-sulfonyl chloride,

0.60 pbw of the esterification product of 1 mole of2,2'-dihydroxy-1,1'-dinaphthylmethane and 2 moles of1,2-naphthoquinone-2-diazide-5-sulfonyl chloride,

5.80 pbw of the novolak indicated in Example 1,

1.00 pbw of the esterification product of 1 mole of4,4'-dihydroxy-3,3'-dinitro-5,5'-dibromobenzophenone and 2 moles of1,2-naphthoquinone-2-diazide-4-sulfonyl chloride,

0.40 pbw of the azo dyestuff indicated in Example 1,

40.00 pbw of ethylene glycol monomethyl ether, and

50.00 pbw of tetrahydrofuran.

Support: electrochemically roughened and anodized aluminum platecorresponding to Example 1.

Color of the exposed areas changed from deep dark blue to yellow brown.

EXAMPLE 4

Coating solution:

0.70 pbw of the esterification product of 1 mole of2,3,4-trihydroxybenzophenone and 2 moles of1,2-naphthoquinone-2-diazide-5-sulfonyl chloride,

0.40 pbw of the esterification product of 1 mole of2,2'-dihydroxy-1,1'-dinaphthylmethane and 2 moles of1,2-naphthoquinone-2-diazide-5-sulfonyl chloride,

6.00 pbw of the novolak indicated in Example 1,

1.00 pbw of the esterification product of 1 mole of3,3'-dibromo-4,4'-dihydroxy-5,5'-dinitroazobenzene and 2 moles of1,2-naphthoquinone-2-diazide-4-sulfonyl chloride,

0.30 pbw of the blue azo dyestuff indicated in Example 2,

40.00 pbw of ethylene glycol monomethyl ether, and

50.00 pbw of tetrahydrofuran.

Support: electrochemically roughened and anodized aluminum platecorresponding to Example 1.

Color of the exposed areas changed from deep dark blue to pale brown.

EXAMPLE 5

Coating solution:

0.70 pbw of the esterification product of 1 mole of2,3,4-trihydroxybenzophenone and 2 moles of1,2-naphthoquinone-2-diazide-5-sulfonyl chloride,

0.40 pbw of the esterification product of 1 mole of2,2'-dihydroxy-1,1'-dinaphthylmethane and 2 moles of1,2-naphthoquinone-2-diazide-5-sulfonyl chloride,

5.80 pbw of the novolak indicated in Example 1,

1.00 pbw of the esterification product of 1 mole of4,4'-dihydroxy-3,5,3',5'-tetranitrodiphenylsulfone and 2 moles of1,2-naphthoquinone-2-diazide-4-sulfonyl chloride,

0.30 pbw of the azo dyestuff indicated in Example 1,

40.00 pbw of ethylene glycol monomethyl ether, and

50.00 pbw of tetrahydrofuran.

Support: electrochemically roughened and anodized aluminum platecorresponding to Example 1.

Color changed from deep dark blue to brown.

EXAMPLE 6

Coating solution:

1.00 pbw of the esterification product of 1 mole of2,3,4-trihydroxybenzophenone and 3 moles of1,2-naphthoquinone-2-diazide-5-sulfonyl chloride,

6.40 pbw of the novolak indicated in Example 1,

0.90 pbw of the esterification product of 1 mole of2,2'-dihydroxy-3,5,3',5'-tetranitrodiphenylmethane and 2 moles of1,2-naphthoquinone-2-diazide-4-sulfonyl chloride,

0.30 pbw of an azo dyestuff obtained by coupling 4-nitro-benzenediazonium salt with diphenylamine,

40.00 pbw of ethylene glycol monomethyl ether, and

50.00 pbw of tetrahydrofuran.

Support: Electrochemically roughened and anodized aluminum platecorresponding to Example 1.

Color of the exposed areas changed from red-brown to black.

EXAMPLE 7

Coating solution:

0.70 pbw of the esterification product of 1 mole of2,3,4-trihydroxybenzophenone and 2 moles of1,2-naphthoquinone-2-diazide-5-sulfonyl chloride,

0.40 pbw of the esterification product of 1 mole of2,2'-dihydroxy-1,1'-dinaphthylmethane and 2 moles of1,2-naphthoquinone-2-diazide-5-sulfonyl chloride,

5.80 pbw of the novolak indicated in Example 1,

0.90 pbw of the esterification product of 1 mole of4,4'-dihydroxy-3,5,3',5'-tetranitrodiphenyl and 2 moles of1,2-naphthoquinone-2-diazide-4-sulfonyl chloride,

0.30 pbw of the azo dyestuff indicated in Example 1,

40.00 pbw of ethylene glycol monomethyl ether, and

50.00 pbw of tetrahydrofuran.

Support: electrochemically roughened and anodized aluminum plate.

Color of the exposed areas changed from blue to brown.

EXAMPLE 8

Coating solution:

1.20 pbw of a 50% strength solution of a polyorthoester in toluene,prepared from 7,7-bis-hydroxymethyl-5-oxanonan-1-ol and trimethylorthoformate,

0.30 pbw of the esterification product of 1 mole of2,2'-dihydroxy-3,5,3',5'-tetranitrodiphenylmethane and 2 moles of1,2-naphthoquinone-2-diazide-4-sulfonyl chloride,

1.00 pbw of the novolak indicated in Example 1,

0.10 pbw of the blue azo dyestuff indicated in Example 1,

20.00 pbw of ethylene glycol monomethyl ether, and

20.00 pbw of tetrahydrofuran.

Support: Electrochemically roughened and anodized aluminum plate.

Color of the exposed areas changed from dark blue to yellow-brown.

EXAMPLE 9

Coating solution:

0.60 pbw of a polyacetal prepared from triethylene glycol and2-ethylbutyraldehyde,

0.30 pbw of the esterification product of 1 mole of4,4'-dihydroxy-3,5,3'-5'-tetranitrodiphenylmethane and 2 moles of1,2-naphthoquinone-2-diazide-4-sulfonyl chloride,

1.00 pbw of the novolak indicated in Example 1,

0.10 pbw of the azo dyestuff indicated in Example 1,

20.00 pbw of ethylene glycol monomethyl ether, and

20.00 pbw of tetrahydrofuran.

Support: Electrochemically roughened and anodized aluminum plate.

Color of the exposed areas changed from blue to pale brown.

What is claimed is:
 1. A light-sensitive mixture, comprising:(a) a1,2-quinonediazide of a mixture of(a¹) a compound forming an acid onexposure and (a²) a compound having at least one C--O--C bond cleavableby acid; (b) a water-insoluble binder soluble in aqueous-alkalinesolution; (c) an organic compound forming an acid on exposure comprisingan ester of the formula I ##STR4## wherein X is a single bond or one ofthe groups CO, SO₂, N=N or CR⁷ R⁸, R¹, R², R³ and R⁴ are hydrogen atoms,halogen atoms or nitro groups, with not more than two of these groupsbeing hydrogen atoms and at least one thereof being a nitro group, R⁵and R⁶ are hydrogen atoms or 1,2-naphthoquinone-2-diazide-4-sulfonyloxyradicals, with R⁵ and R⁶ being always different from each other, and R⁷and R⁸ are hydrogen atoms or lower alkyl radicals, and (d) a dyestuffcomprising an azo dyestuff containing at least one nitro group in themolecule,said ingredients a, b, c, and d being present in such amountsthat said mixture produces after imagewise exposure thereof an image ofan original which is clearly visible under yellow safety light.
 2. Alight-sensitive mixture as claimed in claim 1, wherein R¹ to R⁴ arehalogen atoms or nitro groups.
 3. A light-sensitive mixture as claimedin claim 1, wherein at least 2 of the radicals R¹ to R⁴ are nitrogroups.
 4. A light-sensitive mixture as claimed in claim 1, wherein saiddyestuff comprises a monoazo dyestuff.
 5. A light-sensitive mixture asclaimed in claim 1, wherein said azo dyestuff is present in an amount offrom about 0.5 to 10% by weight relative to the content of nonvolatileconstituents in said mixture.
 6. A light-sensitive mixture as claimed inclaim 1, wherein said binder comprises a novolak resin.
 7. Alight-sensitive mixture as claimed in claim 1, wherein the1,2-quinonediazide comprises a 1,2-naphthoquinone-2-diazidesulfonic acidester.
 8. A light-sensitive mixture as claimed in claim 1, wherein thecompound having at least one C--O--C bond cleavable by acid comprises anorthocarboxylic acid derivative or a compound having at least one acetalgroup in the molecule.
 9. A light-sensitive copying material, comprisinga support and a light-sensitive layer which becomes soluble in adeveloper on light exposure and which layer comprises a light-sensitivemixture as defined by claim 1.